Studies concerning the detoxification of noxious, lipophilic foreign and endogenous compounds through oxidation by monooxygenase activity and/or through conjugation by genetically regulated UDP glucuronosyltransferase activity have continued primarily with 1-hydroxy-, 3-hydroxy-, 9-hydroxy-phenols, and bilirubin. Further studies in which analyses for induction of other types of bilirubin conjugating activities were made indicate that a UDP glucuronosyltransferase activity is responsible for genetically regulated induction of bilirubin conjugating activity. Purification of UDP glucuronosyltransferase activity is markedly improved by using a phosphate buffer system including 20% glycerol with hydrophobic and hydroxyapatite columns which enhance the removal of cytochrome P-450 which is present in much higher levels in microsomes than is the UDP glucuronosyltransferase enzyme(s). Preliminary studies with the antiseizure drug valproic acid indicate that immature mice clear the drug from the blood more slowly than mature animals and develop complete loss of hair from the body after one of week of daily injections at a dose consistent with a human dose.